Encrypt outgoing emails when possible

app/mailers/application_mailer.rb

@@ -1,3 +1,89 @@
 class ApplicationMailer < ActionMailer::Base
   layout 'mailer'
+
+  private
+
+    def send_mail
+      @template ||= "#{self.class.name.underscore}/#{caller[0][/`([^']*)'/, 1]}"
+      headers['Message-ID'] = message_id
+
+      if @user.pgp_pubkey.present?
+        mail(to: @user.email, subject: "...", content_type: pgp_content_type) do |format|
+          format.text { render plain: pgp_content }
+        end
+      else
+        mail(to: @user.email, subject: @subject) do |format|
+          format.text { render @template }
+        end
+      end
+    end
+
+    def from_address
+      ENV.fetch('SMTP_FROM_ADDRESS', 'accounts@localhost')
+    end
+
+    def from_domain
+      Mail::Address.new(from_address).domain
+    end
+
+    def message_id
+      @message_id ||= "#{SecureRandom.uuid}@#{from_domain}"
+    end
+
+    def boundary
+      @boundary ||= SecureRandom.hex(8)
+    end
+
+    def pgp_content_type
+      "multipart/encrypted; protocol=\"application/pgp-encrypted\"; boundary=\"------------#{boundary}\""
+    end
+
+    def pgp_nested_content
+      message_content = render_to_string(template: @template)
+      message_content_base64 = Base64.encode64(message_content)
+      nested_boundary = SecureRandom.hex(8)
+
+      <<~NESTED_CONTENT
+        Content-Type: multipart/mixed; boundary="------------#{nested_boundary}"; protected-headers="v1"
+        Subject: #{@subject}
+        From: <#{from_address}>
+        To: #{@user.display_name || @user.cn} <#{@user.email}>
+        Message-ID: <#{message_id}>
+
+        --------------#{nested_boundary}
+        Content-Type: text/plain; charset=UTF-8; format=flowed
+        Content-Transfer-Encoding: base64
+
+        #{message_content_base64}
+
+        --------------#{nested_boundary}--
+      NESTED_CONTENT
+    end
+
+    def pgp_content
+      encrypted_content = UserManager::PgpEncrypt.call(user: @user, text: pgp_nested_content)
+      encrypted_base64 = Base64.encode64(encrypted_content.to_s)
+
+      <<~EMAIL_CONTENT
+        This is an OpenPGP/MIME encrypted message (RFC 4880 and 3156)
+        --------------#{boundary}
+        Content-Type: application/pgp-encrypted
+        Content-Description: PGP/MIME version identification
+
+        Version: 1
+
+        --------------#{boundary}
+        Content-Type: application/octet-stream; name="encrypted.asc"
+        Content-Description: OpenPGP encrypted message
+        Content-Disposition: inline; filename="encrypted.asc"
+
+        -----BEGIN PGP MESSAGE-----
+
+        #{encrypted_base64}
+
+        -----END PGP MESSAGE-----
+
+        --------------#{boundary}--
+      EMAIL_CONTENT
+    end
 end

app/mailers/custom_mailer.rb

@@ -18,6 +18,6 @@ class CustomMailer < ApplicationMailer
     @user = params[:user]
     @subject = params[:subject]
     @body = params[:body]
-    mail(to: @user.email, subject: @subject)
+    send_mail
   end
 end

app/mailers/notification_mailer.rb

@@ -3,7 +3,7 @@ class NotificationMailer < ApplicationMailer
     @user = params[:user]
     @amount_sats = params[:amount_sats]
     @subject = "Sats received"
-    mail to: @user.email, subject: @subject
+    send_mail
   end
 
   def remotestorage_auth_created
@@ -15,19 +15,19 @@ class NotificationMailer < ApplicationMailer
       "#{access} #{directory}"
     end
     @subject = "New app connected to your storage"
-    mail to: @user.email, subject: @subject
+    send_mail
   end
 
   def new_invitations_available
     @user = params[:user]
     @subject = "New invitations added to your account"
-    mail to: @user.email, subject: @subject
+    send_mail
   end
 
   def bitcoin_donation_confirmed
     @user = params[:user]
     @donation = params[:donation]
     @subject = "Donation confirmed"
-    mail to: @user.email, subject: @subject
+    send_mail
   end
 end

app/services/user_manager/pgp_encrypt.rb

@@ -0,0 +1,19 @@
+require 'gpgme'
+
+module UserManager
+  class PgpEncrypt < UserManagerService
+    def initialize(user:, text:)
+      @user = user
+      @text = text
+    end
+
+    def call
+      crypto = GPGME::Crypto.new
+      crypto.encrypt(
+        @text,
+        recipients: @user.gnupg_key,
+        always_trust: true
+      )
+    end
+  end
+end

spec/mailers/notification_mailer_spec.rb

@@ -0,0 +1,87 @@
+# spec/mailers/welcome_mailer_spec.rb
+require 'rails_helper'
+
+RSpec.describe NotificationMailer, type: :mailer do
+  describe '#lightning_sats_received' do
+
+    context "without PGP key" do
+      let(:user) { create(:user, cn: "phil", email: 'phil@example.com') }
+
+      before do
+        allow_any_instance_of(User).to receive(:ldap_entry).and_return({
+          uid: user.cn, ou: user.ou, display_name: nil, pgp_key: nil
+        })
+      end
+
+      describe "unencrypted email" do
+        let(:mail) { described_class.with(user: user, amount_sats: 21000).lightning_sats_received }
+
+        it 'renders the correct to/from headers' do
+          expect(mail.to).to eq([user.email])
+          expect(mail.from).to eq(['accounts@kosmos.org'])
+        end
+
+        it 'renders the correct subject' do
+          expect(mail.subject).to eq('Sats received')
+        end
+
+        it 'uses the correct content type' do
+          expect(mail.header['content-type'].to_s).to include('text/plain')
+        end
+
+        it 'renders the body with correct content' do
+          expect(mail.body.encoded).to match(/You just received 21,000 sats/)
+          expect(mail.body.encoded).to include(user.address)
+        end
+
+        it 'includes a link to the lightning service page' do
+          expect(mail.body.encoded).to include("https://accounts.kosmos.org/services/lightning")
+        end
+      end
+    end
+
+    context "with PGP key" do
+      let(:pgp_pubkey) { File.read("#{Rails.root}/spec/fixtures/files/pgp_key_valid_alice.asc") }
+      let(:pgp_fingerprint) { "EB85BB5FA33A75E15E944E63F231550C4F47E38E" }
+      let(:user) { create(:user, id: 2, cn: "alice", email: 'alice@example.com', pgp_fpr: pgp_fingerprint) }
+
+      before do
+        allow_any_instance_of(User).to receive(:ldap_entry).and_return({
+          uid: user.cn, ou: user.ou, display_name: nil, pgp_key: pgp_pubkey
+        })
+      end
+
+      describe "encrypted email" do
+        let(:mail) { described_class.with(user: user, amount_sats: 21000).lightning_sats_received }
+
+        it 'renders the correct to/from headers' do
+          expect(mail.to).to eq([user.email])
+          expect(mail.from).to eq(['accounts@kosmos.org'])
+        end
+
+        it 'encrypts the subject line' do
+          expect(mail.subject).to eq('...')
+        end
+
+        it 'uses the correct content type' do
+          expect(mail.header['content-type'].to_s).to include('multipart/encrypted')
+          expect(mail.header['content-type'].to_s).to include('protocol="application/pgp-encrypted"')
+        end
+
+        it 'renders the PGP version part' do
+          expect(mail.body.encoded).to include("Content-Type: application/pgp-encrypted")
+          expect(mail.body.encoded).to include("Content-Description: PGP/MIME version identification")
+          expect(mail.body.encoded).to include("Version: 1")
+        end
+
+        it 'renders the encrypted PGP part' do
+          expect(mail.body.encoded).to include('Content-Type: application/octet-stream; name="encrypted.asc"')
+          expect(mail.body.encoded).to include('Content-Description: OpenPGP encrypted message')
+          expect(mail.body.encoded).to include('Content-Disposition: inline; filename="encrypted.asc"')
+          expect(mail.body.encoded).to include('-----BEGIN PGP MESSAGE-----')
+          expect(mail.body.encoded).to include('hF4DR')
+        end
+      end
+    end
+  end
+end